The Organic Light Emitting Display (OLEO) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types according to the driving ways, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution.
The AMOLED is a current driving element. When the electrical current flows through the organic light emitting diode, the organic light emitting diode emits light, and the brightness is determined according to the current flowing through the organic light emitting diode itself. Most of the present Integrated Circuits (IC) only transmits voltage signals. Therefore, the AMOLED pixel driving circuit needs to accomplish the task of converting the voltage signals into the current signals. Usually, there has a drive TFT for driving OLED to emitting in AMOLED pixel drive circuit. In use, because of aging of OLED and shift of a threshold voltage of the driving TFT, which causes the display quality of OLED display device be decreased so that needs to detect threshold voltage of drive TFT in using and compensates it for ensure the display quality of OLED display device.
Compensation technology of AMOLED can be categorized into two major types of internal compensation and external compensation, most of all needs more TFT to achieve compensation. Therefore, it needs more scanning drive signal, especially for the internal compensation, and design of the gate drive circuit play a key factor for that. More complicated internal compensation more scanning signal be needed, and a huge number of scanning signals let Drive IC and panel circuit design bring a serious problem, and increase cost of panel.